M2, Globular Cluster in Aquarius
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| M2 (NGC 7089) | Globular Cluster | 21h 33m 27s | -00° 49′ 24″ | Aquarius | +6.5 | 16.0 arcmins |
Overview
Our first challenge this month is to find the second object in Charles Messier’s catalog. Although he discovered it independently, he wasn’t the first astronomer to point a telescope in its direction. Jean-Dominique Maraldi holds that honor, documenting his observation of it on September 11, 1746. It was exactly four years later – to the day – that Charles Messier observed this tight knot of stars for himself.
M2 is a spectacular object. It is some 175 light-years wide and contains over 150,000 stars! And, it is old. It’s oldest red giant stars are thought to have been burning their fuel for 13 billion years or more.
The cluster is located roughly midway between us and the center of our Milky Way galaxy, being roughly 35,000 light-years away from each. As one of the oldest and largest clusters in the Milky Way, it makes a glorious sight in our backyard telescopes.
Finder Charts
M2 is bright enough that you will glimpse it through a magnifying finderscope if you’re sky is relatively dark. It will look like a slightly out of focus star. Otherwise, we’re going to use the rather unremarkable stars of Aquarius to hunt it down.
The first SkySafari 6 chart below shows the general area of the sky we’re looking in. This is the view at 7pm in the middle of November. The Moon and planets are not shown to aid clarity in your search. Note how the limb of Pegasus extending from Markab in the Great Square of Pegasus points in the direction of M2.
The easiest ways to find M2 are to use the limb from Markeb, shown in orange below, or form a right-angled triangle with M2, Sadalmelik, and Sadalsuud, as shown in green.
In this final image, which covers the same part of the sky as above, stars are shown to magnitude 7.0 and the route from Baham is shown in 5° hops (large blue circle) which is roughly the area of sky in a finderscope. The small blue circle around M2 itself is a 1° field of view.
When you’ve successfully placed M2 in your eyepiece, what should you expect to see?
Individual Telescope Views
The following views will help you find M2 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Each image can be clicked on for a full-screen version.
Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope
Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal
Mirrored View – Refractors and Cassegrain models with a star diagonal show this view
Observation
M2 is so bright that is on the edge of naked eye visibility. If you have great eyesight and a very dark sky, you could just about see its glow without a telescope or binoculars!
As it is, almost all of us will need an optical aid to find it, but what a view when you do!
M2 resides in a relatively barren area of the sky, so there is little in the way of background stars to distract you from its glory when you’ve centered it. Smaller telescopes at low power reveal it as a glowing area of brightness, with the core so bright it is star-like. At this level, there is no teasing out individual stars within the mass.
Increasing your magnification will begin to tease out the more remote and brighter members of the cluster. These shine at around magnitude 13 and are distinguishable in telescopes larger than 4″ with magnifications over 70x.
Look at the shape of the cluster. It’s easy to see it as circular when viewed at lower magnifications but zooming in reveals this is not the case. Instead, it appears more oval, with the longer axis on a north-south axis.
One other aspect to look for, which requires patience and maybe some experience, is the presence of shadows. Do you see any of these? They’re like dark arms in between the whorls of stars.
Challenge yourself to count as many individual stars as possible.
PDFs for Printing
Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [M2-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.